Electrostatic precipitator with means for the enhanced charging and collection of fine particles

Abstract

An electrical precipitator which uses a combination of field charging, diffusion charging, and electron charging for the enhancement of fine particle charging and collection. A precipitator is described for the collection of fine particles of less than 1.0 micron in diameter from an effluent by enhancing the charge thereon by electrons of high kinetic energy. Another feature of the invention describes a precharging stage which can be added to the electron charging stage, or other conventional precipitator stage, that operates the basis of ion bombardment or diffusion of thermally active ions. The precharging stage charges the fine particles and they can later be increased in charge and precipitated by the electron charging stage. Another feature of the invention describes disposing a conventional stage for coarse particulates over 1.0 micron in diameter between the diffusion charging stage and the electron charging stage.

What is claimed is: 
     
       1. An electrostatic precipitator having multiple stages for precipitating particulate matter from an effluent gas, comprising: means forming a first stage for precharging fine particulate matter suspended in said effluent primarily by diffusion charging;   means forming a second stage for charging and precipitating coarse particulate matter suspended in said effluent primarily by field charging; and   means forming a third stage for increasing the charge on and precipitating said fine particulate matter suspended in said effluent primarily by electron charging   
     
     
       2. An electrostatic precipitator as defined in claim 1, wherein said means for forming a third stage include: a plurality of precipitator elements, each including a pair of substantially parallel collection plates used as an anode and forming a channel through which effluent passes and at least one wire acting as a cathode for generating electrons by corona discharge located between said plates to charge said fine particulate matter, said collection plates spaced apart from each other a distance allowing the optimum exposure of said fine particulate matter to said electrons; and   a plurality of pulsed power supplies, each connected to at least a respective one of said precipitator elements at its cathode, for generating periodic high voltage pulses at a repetition rate and peak voltage sufficient to generate a large number of electrons at a high kinetic energy to charge said fine particulate matter and for maintaining a substantially constant collection voltage between said cathode and said collection plates in the interval between pulses.   
     
     
       3. An electrostatic precipitator as defined in claim 2 wherein: the spacing between said collection plates is 4 inches.   
     
     
       4. An electrostatic precipitator as defined in claim 2 wherein: the peak voltage of said high voltage pulses is between -15 and -25 kV.   
     
     
       5. An electrostatic precipitator as defined in claim 2 wherein: the interval between said high voltage pulses is between 2-20 millisecs.   
     
     
       6. An electrostatic precipitator as defined in claim 2 therein: said collection voltage produces a collection field between said plates which is in excess of -14 kV/cm.   
     
     
       7. An electrostatic precipitator as defined in claim 2 wherein: said high voltage pulses have a pulse width of between 30-200 microseconds.   
     
     
       8. An electrostatic precipitator as defined in claim 2 wherein: said fine particulate matter generally has a diameter of less than one micron.   
     
     
       9. An electostatic precipitator as defined in claim 1, wherein said means for form:ing a first stage include: a plurality of precipitator elements, each including a pair of spaced, substantially parallel collection plates used as an anode and forming a channel through which effluent passes and at least one wire acting as a cathode for generating electrons by corona discharge located between said plates to charge the fine particulate matter, said electrons charging gas molecules of said effluent to become ions; and   a plurality of pulsed of power suplies, each connected to at least a respective one of said precipitator elements at its cathode, for generating periodic high voltage pulses at a repetition rate and peak voltage sufficient to generate a large number of electrons and thereby ions to charge said fine particulate matter and at a minimal time average field to optimize ion life time.   
     
     
       10. An electrostatic precipitator as defined in claim 9 wherein: the spacing between said collection plates is 4 inches.   
     
     
       11. An electrostatic precipitator as defined in claim 9 wherein: the peak voltage of said high voltage pulses is between -15 and -25 kv.   
     
     
       12. An electrostatic precipitator as defined in claim 9 wherein: the interval between said high voltage pulses is between 2-20 milliseconds.   
     
     
       13. an electrostatic precipitator as defined in claim 9 wherein: said high voltage pulses have a pulse width of between 30-200 microseconds.   
     
     
       14. An electrostatic precipitator as defined in claim 1, wherein said means for forming a second stage include: a plurality of precipitator elements, each including a pair of substantially parallel collection plates used as an anode and forming a channel through which effluent passes and at least one wire acting as a cathode for generating electrons by corona discharge located between said plates to charge said coarse particulate matter, said electrons charging gas molecules of said effluent to become ions and said collection plates spaced apart from each other a distance allowing the optimum exposure of said coarse particulate matter to said ions; and   a plurality of pulsed power supplies, each connected to at least a respective one of said precipitator elements at its cathode, for generating periodic high voltage pulses at a repetition rate and peak voltage sufficient to generate a large number of electrons and thereby ions to charge said coarse particulate matter and for maintaining a substantially constant collection voltage between said cathode and said collection plates in the interval between pulses.   
     
     
       15. An electostatic precipitator as defined in claim 14 wherein: said spacing between said collection plates is approximately 4.5 inches.   
     
     
       16. An electrostatic precipitator as defined in claim 14 wherein: the peak voltage of said high voltage pulses is between -15 and -25 kV.   
     
     
       17. An electrostatic precipitator as defined in claim 14 wherein: the interval between said high voltage pulses is between 2-20 millisecs.   
     
     
       18. An electrostatic precipitator as defined in claim 14 wherein: said collection voltage is in excess of 4 kV/cm.   
     
     
       19. An electrostatic precipitator as defined in claim 14 wherein: said high voltage pulses have a pulse width of between 30-200 microsecs.   
     
     
       20. An electrostatic precipitator having multiple stages for precipitating particulate matter from an effluent gas, comprising: means forming a first stage for precharging fine particulate matter suspended in said effluent primarily by diffusion charging; and   means forming a second stage for charging coarse particulate matter suspended in said effluent primarily by field charging and for precipitating said precharged fine particulate matter and said charged coarse particulate matter.   
     
     
       21. An electrostatic precipitator as defined in claim 20, wherein said means for forming a first stage include: a plurality of precipitator elements, each including a pair of substantially parallel collection plates used as an anode and forming a channel through which effluent passes and at least one wire acting as a cathode for generating electrons by corona discharge located between said plates to charge the fine particulate matter, said electrons charging gas molecules of said effluent to become ions;   a plurality of pulsed power supplies, each connected to at least a respective one of said precipitator elements at its cathode, for generating periodic high voltage pulses at a repetition rate and peak voltage sufficient to generate a large number of electrons and thereby ions to charge said fine particulate matter and at a minimal time average field to optimize ion life time.   
     
     
       22. An electrostatic precipitator as defined in claim 20, wherein said means for forming a second stage include: a plurality of precipitator elements, each including a pair of substantially parallel collection plates used as an anode and forming a channel through which effluent passes and at least one wire acting as a cathode for generating electrons by corona discharge located between said plates to charge said coarse particulate matter, said electrons charging gas molecules of said effluent to become ions and said collection plates spaced apart from each other a distance allowing the optimum exposure of said coarse particulate matter to said ions; and   a plurality of pulsed power supplies, each connected to at least a respective one of said precipitator elements at its cathode, for generating periodic high voltage pulses at a repetition rate and peak voltage sufficient to generate a large number of electrons and thereby ions to charge said coarse particulate matter and for maintaining a substantially constant collection voltage between said cathode and said collection plates in the interval between pulses.   
     
     
       23. an electrostatic precipitator having multiple stages for precipitating particulate matter from an effluent gas, comprising: means forming a first stage for precharging fine particulate matter suspended in said effluent primarily by diffusion charging; and   means forming a second stage for increasing the charge on and precipitating said fine particulate matter suspended in said effluent primarily by electron charging.   
     
     
       24. An electrostatic precipitator as defined in claim wherein said means for forming a first stage include: a plurality of precipitator elements, each including a pair of substantially parallel collection plates used as an anode and forming a channel through which effluent passes and at least one wire acting as a cathode for generating electrons by corona discharge located between said plates to charge the fine particulate matter, said electrons charging gas molecules of said effluent to become ions; and   a plurality of pulsed power supplies, each connected to at least a respective one of said precipitator elements at its cathode, for generating periodic high voltage pulses at a repetition rate and peak voltage sufficient to generate a large number of electrons and thereby ions to charge said fine particulate matter and at a minimal time average field to optimize ion life time.   
     
     
       25. An electrostatic precipitator as defined in claim 23, wherein said means for forming a second stage include: a plurality of precipitator elements, each including a pair of substantially parallel collection plates used as an anode and forming a channel through which effluent passes and at least one wire acting as a cathode for generating electrons by corona discharge located between said plates to charge said fine particulate matter, said collection plates spaced apart from each other a distance allowing the optimum exposure of said fine particulate matter to said electrons; and   a plurality of pulsed power supplies, each connected to at least a respective one of said precipitator elements at its cathode, for generating periodic high voltage pulses at a repetition rate and peak voltage sufficient to generate a large number of electrons at a high kinetic energy to charge said fine particulate matter and for maintaining a substantially constant collection voltage between said cathode and said collection plates in the interval between pulses.